Interpretive Summary: The soybean aphid has been a major insect pest of soybean in the United States since 2000. Identification and genetic characterization of plant resistance to soybean aphid in early maturing soybean will facilitate development of aphid-resistant soybean lines for the northern production region. To identify new sources of resistance in early maturing soybeans, a total of 334 soybean lines including resistant and susceptible checks were tested in the greenhouse and field. In the field, only PI 603712 was resistant and PI 430491 was moderately resistant, each with fewer than 200 aphids per plant at peak infestation. PI 603712 was only the soybean line that consistently showed resistance to soybean aphid in all tests, even higher than that of other known sources of SA resistance in the field. This suggests that PI 603712 may be a new source of resistance.

Technical Abstract:
Soybean aphid (SA, Aphis glycines Matsumura) has been an important pest of soybean (Glycine max (L.) Merr.) in the United States since 2000. Identification and genetic characterization of SA resistance in early maturing soybean germplasm will facilitate development of aphid-resistant cultivars in northern region. To identify new sources of SA resistance in early maturing soybeans, a total of 334 soybean genotypes including resistant and susceptible checks were tested in the greenhouse and field. In the field, only PI 603712 was resistant, and PI 430491 exhibited moderate resistance, with fewer than 100 or 100-200 aphids per plant at peak infestation, respectively. PI 603712 was the only genotype which consistently exhibited resistance to SA in all tests, even higher than that of other known sources of SA resistance in the field. This suggests that PI 603712 might be a new source of SA resistance.